1. Field of the Invention
The present invention is concerned with a method for adhering curved tensioned strips of elastic material to a gatherable base material in order to elasticize portions of the base material, and is also concerned with the elasticized article thereby obtained. The invention finds particular application in elasticizing garments, in particular in elasticizing disposable incontinence control garments, for example, disposable diapers. The manufacture of such articles is usually carried out by joining continuous moving webs of material to form a composite web which is then cut transversely to form the individual articles. It is often desired to elasticize portions of the garments, such as the leg cut-out portions of disposable diapers, in order to provide a snug fit of the diaper about the wearer's legs to aid in controlling or preventing leakage. It is a common expedient in the art to. apply bands of elastic material under tension to a moving web or webs of material, utilizing an adhesive, electronic welding, mechanical stitching or any suitable means to secure the tensioned elastic band to the web. Because the elastic band is glued or otherwise secured to the web while held in a tensioned, elongated condition, upon cutting of the web into individual articles the tensioned, elongated elastic bands relax to form elasticized gathers in the flexible material. Generally, any suitable elastic material comprising a suitable rubber, synthetic organic polymeric material or composite material may be utilized as the elastic band.
2. Description of the Related Art
A particularly useful material for the elastic bands would be one which is both elastic and self-adhering to the gatherable base material which is to be elasticized. Such self-adhering elastic materials are known and obviate the need for separate gluing or other steps to secure the elastic bands to the gatherable base material. For example, U.S. Pat. No. 4,259,220 and related U.S. Pat. No. 4,418,123, respectively disclose (1) a viscoelastic, hot melt, pressure sensitive adhesive which can be extruded to form a tape which is both pressure sensitive adhesive and elastic, and (2) a method for imparting elastic properties to a flexible substrate by contacting a surface of the substrate with the specified self-adhering elastic material. The disclosure of each of U.S. Pat. No. 4,259,220, issued Mar. 31, 1981 to William L. Bunnelle et al, and U.S. Pat. No. 4,418,123, issued Nov. 29, 1983 to William L. Bunnelle et al, is incorporated by reference herein.
U.S. Pat. No. 4,023,571 discloses the manufacture of an absorbent undergarment utilizing an absorbent first layer having the property of elastic recovery, which is described as the capability of being elongated under tensile stress and at least partially recovering from the elongation upon release of the tensile stress. A relatively inelastic second layer or member (26 in FIG. 3) is adhered to the first layer (16 in FIG. 3) in laterally coextensive and mutally centered relationship while the first member is held longitudinally under tension. Upon release of the tension the flat laminate gradually acquires an arcuate shape (FIGS. 4 and 5 and items 10, 10' in FIG. 6) as the elastic recovery forces of absorbent layer 26 are resisted by the relatively inelastic second layer 28. See Column 6, lines 3-27. The arcuate shape results from bowing of the laminated layers out of their original flat plane in a direction perpendicular thereto.
The application of bands of elastic material under tension to a moving web of material, as is practiced in the manufacture of items such as disposable diapers, presents difficulties including those which arise from the fact that the webs of material are usually traveling at high rates of speed, for example, from 500 to 600 feet per minute. These high web speeds are required for efficient manufacture but make it difficult to adhere elastic strips to the moving web, particularly if it is sought to do so in other than a straight linear configuration of the elastic strips. Another difficulty is that self-adhering elastic materials of the type described in the aforementioned Bunnelle et al U.S. patents is that, at least with respect to certain base materials such as the polyolefin sheet materials normally used in disposable diaper manufacture, the greater the degree to which the self-adhering elastic materials are elongated when applied to the base material, the less adherent to the base material do the elastic materials become. In other words, the greater the degree of elongation to which the self-adhering elastic materials are subjected upon being adhered to the polyolefin base material, the more is the self-adhering power of the elastic material reduced. One solution to the latter problem is set forth in co-pending patent application Ser. No. 676,920 (now U.S. Pat. No. 4,556,596) of Michael G. Meuli, filed Nov. 30, 1984, and entitled " Method for Adhering Tensioned Elastic Strips to a Gatherable Base Material", in which the tensioned strip of self-adhering elastic material is secured to the moving web of base material by a second, less or untensioned strip of self-adhering elastic material.